Sulfuryl fluoride (SO.sub.2 F.sub.2) is a well-known fumigant which is prepared by the reaction of sulfur dioxide (SO.sub.2), chlorine (Cl.sub.2) and hydrogen fluoride (HF) at elevated temperatures over an activated catalyst. See U.S. Pat. No. 3,092,458, and 2,772,144. In the processes of the type disclosed in these patents, high yields of good quality SO.sub.2 F.sub.2 readily obtainable at the outset of such operations. However, apparently as the result of side reactions, the activated carbon catalyst becomes rapidly poisoned, resulting in commercial disadvantages such as short catalyst life, low weight recovery of SO.sub.2 F.sub.2 per weight unit of catalyst used and rapid decrease of product yield and quality as the poisoning of the catalyst progresses.
U.S. Pat. No. 3,320,030 discloses that a mixture of activated charcoal and an alkali metal bifluoride effectively catalyzes the reaction and does not poison as quickly as the activated charcoal alone. This catalyst system appears to be effective; however, it suffers from the disadvanages that material still must be removed from the reactor and replaced with fresh catalyst every 60 to 100 hours of operation or else regenerated. This is a slow process as the reactor has to be cooled and the spent catalyst, which contains considerable corrosive HF, is difficult to handle and dispose.
An alternative method of increasing catalyst life is regeneration. The standard method of regenerating an activated charcoal catalyst by partial oxidation with high temperature steam, has the disadvantage of eventually destroying the catalyst both by direct oxidation and degradation of the catalyst particles into fines.
Another method for regenerating the activated charcoal catalyst is disclosed in U.S. Pat. No. 3,714,336 and involves reducing the spent catalyst with a hydrogen stream at 400.degree.-800.degree. C. However, such method has the disadvantage of the need to purge the catalyst prior to and after regeneration with hydrogen and to scrub the vented hydrogen gas to remove HF and other by-products therefrom prior to release.
It would thus be desirable and it is an object of the present invention to provide a new method for the regeneration of the activated charcoal catalyst used in the reaction of SO.sub.2, Cl.sub.2, and HF to produce SO.sub.2 F.sub.2 which obviates the disadvantages of the prior art.
An additional object is to provide such a method which preserves the catalyst structure and strength while yielding a regenerated catalyst which has improved activity and cycle life.